As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries as an energy source has also sharply increased.
Depending upon kinds of external devices in which secondary batteries are used, the secondary batteries may be used in the form of a single battery or in the form of a battery pack having a plurality of unit cells electrically connected to one another. For example, small-sized devices, such as mobile phones, can be operated for a predetermined period of time with the power and the capacity of one battery. On the other hand, a battery pack needs to be used in middle or large-sized devices, such as laptop computers, portable digital versatile disc (DVD) players, small-sized personal computers (PCs), electric vehicles and hybrid electric vehicles, because high power and large capacity are necessary for the middle or large-sized devices.
A battery pack is manufactured by connecting a protection circuit to a core pack having a plurality of unit cells (secondary batteries) connected in series and/or in parallel to each other. In a case in which prismatic batteries or pouch-shaped batteries are used as the unit cells, the prismatic batteries or the pouch-shaped batteries are stacked so that large-sized surfaces of the prismatic batteries or the pouch-shaped batteries face each other, and then electrode terminals of the prismatic batteries or the pouch-shaped batteries are connected to each other by connection members, such as bus bars. In a case in which a three-dimensional secondary battery pack having a hexahedral structure is to be manufactured, therefore, the prismatic secondary batteries or the pouch-shaped secondary batteries are preferably used as unit cells of the battery pack.
On the other hand, cylindrical secondary batteries generally have larger electric capacities than the prismatic secondary batteries or the pouch-shaped secondary batteries. However, it is difficult to arrange the cylindrical secondary batteries in a stacked structure due to the external shape of the cylindrical secondary batteries. In a case in which a secondary battery pack is configured generally in a line type structure or in a plane type structure, though, the cylindrical secondary batteries are structurally more advantageous than the prismatic batteries or the pouch-shaped batteries.
Consequently, a battery pack having a plurality of cylindrical secondary batteries connected in series or in parallel and series to each other is widely used in laptop computers, portable DVD players and portable PCs. The battery pack may be configured in various core pack structures. For example, the core pack of the battery pack may be generally configured in a 2P (parallel)-3S (series) line type structure, a 2P-3S plane type structure, a 2P-4S line type structure, a 2P-4S plane type structure, a 1P-3S line type structure or a 1P-3S plane type structure.
The parallel connection structure is achieved by arranging two or more cylindrical secondary batteries in the lateral direction thereof so that the cylindrical batteries are adjacent to each other in a state in which electrode terminals of the cylindrical secondary batteries are oriented in the same direction and connecting the electrode terminals of the cylindrical batteries to each other via connection members by welding. The cylindrical batteries connected in parallel to each other may be referred to as a “bank.”
The series connection structure is achieved by arranging two or more cylindrical secondary batteries in the longitudinal direction thereof so that electrode terminals of the cylindrical secondary batteries having opposite polarities are successively disposed one after another, or arranging two or more cylindrical secondary batteries in the lateral direction thereof so that the cylindrical secondary batteries are adjacent to each other in a state in which electrode terminals of the cylindrical secondary batteries are oriented in opposite directions, and connecting the electrode terminals of the cylindrical secondary batteries to each other via connection members by welding.
The electrical connection between the cylindrical secondary batteries is generally achieved by spot welding using thin connection members (for example, metal plates), such as nickel plates.
FIG. 1 is a typical view illustrating a state in which a battery pack is configured in a 2P-3S plane type structure after electrical connection is completed using spot welding. For easy understanding, a coupling relation of the battery pack configured in the 2P-3S plane type structure is shown as an exploded view in FIG. 1.
As shown in FIG. 1, three pairs of secondary batteries 20 and 21, which are connected in parallel to each other for each pair, are connected in series to each other via metal plates 30 to constitute a core pack 10.
FIG. 2 is a typical view illustrating a battery module 50 in which a protection circuit module is connected to the core pack of FIG. 1.
As shown in FIG. 2, the secondary batteries 20 and 21 are connected to the protection circuit module 90 via a cathode lead wire 60, an anode lead wire 70 and a flexible printed circuit board (FPCB) 80 connected to the metal plates 300. The electrical connection of the protection circuit module 90 to the metal plates 30 is achieved mainly by soldering.
Generally, a battery pack using secondary batteries as unit cells is repeatedly charged and discharged during the use of the battery pack, and the battery pack uses lithium secondary battery, which exhibits low safety in abnormal conditions, such as external impact, dropping, penetration of a needle-shaped body, overcharge, overcurrent, etc., as a unit cell. In order to solve such a safety-related problem, therefore, a safety element, such as a protection circuit module, is included in the battery pack. The safety element acquires information, such as voltage, at a corresponding terminal connection region of the battery pack to perform a predetermined safety process, thereby securing the safety of the battery pack.
Also, safety of the second batteries is greatly lowered at low temperature. For this reason, a temperature detection member is mounted on a unit cell to measure the temperature of the unit cell, and the operation of the battery pack is controlled through the safety element, such as the protection circuit module, based on information obtained from the temperature detection member.
The temperature detection member is fixed to the outside of the unit cell by a bonding agent or an adhesive tape so that the temperature detection member can stably measure the temperature of the unit cells.
However, such a process of attaching the temperature detection member to the outside of the unit cell using the bonding agent or the adhesive tape is troublesome and complicates a process of manufacturing a battery pack.
Also, the temperature detection member attached to the outside of the unit cell using the bonding agent or the adhesive tape may be separated from the outside of the unit cell due to various causes, such as moisture, temperature change or external impact, with the passage of time with the result that a temperature detecting function of the temperature detection member may be deteriorated.
Consequently, there is a high necessity for a technology that is capable of improving manufacturing efficiency of a battery pack and maintaining a state in which the temperature detection member is stably mounted to the unit cells even under abnormal conditions, such as moisture, temperature change or external impact.